| Year | Value | | 2021 | 5.8598506553662 | | 2020 | 6.2482159528414 | | 2019 | 5.5714784401105 | | 2018 | 5.4311280888713 | | 2017 | 4.8915393263398 | | 2014 | 4.6186531335395 | | 2013 | 4.6801061530905 | | 2012 | 4.7475692215632 | | 2011 | 4.8592041174933 | | 2010 | 4.6948501506055 | | 2009 | 5.3437398968046 | | 2008 | 5.0542747080279 | | 2007 | 4.9100106398426 | | 2006 | 5.214387777283 | | 2005 | 5.5523079469988 | | 2004 | 5.5289552303462 | | 2003 | 5.7149953636672 | | 2002 | 5.6795730932496 | | 2001 | 5.3343401513722 | | 2000 | 5.1655393718848 | | 1999 | 5.3609062723511 | | 1998 | 5.078289420189 | | 1997 | 4.8239014710259 | | 1996 | 4.5374354875813 | | 1995 | 4.4949378554503 | | 1994 | 3.9218098962475 | | 1993 | 3.6972072415907 | | 1992 | 3.5959161213815 | | 1991 | 2.8593704314621 |
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